05000388/LER-2017-001

, both airlock doors of a secondary containment airlock were momentarily open at the same time causing an alarm. The event occurred at the Unit 2 airlock between the Turbine Building (TB) and Reactor Building (RB) on Elevation 676. Individuals on the TB side of the airlock verified a green light and opened the TB side door, causing the RB side door to pop open from differential pressure. The individual on the RB side, who was using the security card reader, saw the RB door pop open. The doors were immediately closed, reestablishing secondary containment.

The cause was determined to be sticking of the door latch inside the crash bar, which prevented the RB side airlock door from properly latching and staying latched when differential pressure was applied, such as when the TB side door was opened. Corrective action included replacing the crash bar on the RB side door.

There were no actual consequences to the health and safety of the public as a result of this event.

LER-2017-001, Secondary Containment Declared Inoperable Due to Airlock Doors Open Due to Sticking Door Latch

Event date:

06-1-2017

Report date:

05-65-2017

"05-65-2017" contains a sequence that could not be interpreted against an available match matrix for date components.

comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

2017 - 00

Contents

CONDITIONS PRIOR TO EVENT

Unit 1 — Mode 1, approximately 100 percent Rated Thermal Power Unit 2 — Mode 5, approximately 0 percent Rated Thermal Power There were no structures, systems, or components that were inoperable at the start of the event that contributed to the event.

EVENT DESCRIPTION

On March 6, 2017 at approximately

1325 hours

0.0153 days 0.368 hours 0.00219 weeks 5.041625e-4 months

, both airlock doors [EIIS Component Identifier: DR] of a secondary containment airlock [EIIS System/Component Identifier: NG/AL] were momentarily open at the same time causing an alarm [EIIS Component Identifier: ALM]. The following provides details of the event:

The event occurred at the Unit 2 airlock between the turbine building (TB) [EIIS System Identifier: NM] and reactor building (RB) [EIIS System Identifier: NG] on Elevation 676. Individuals on the TB side of the airlock verified a green light and opened the TB side door, causing the RB side door to pop open from differential pressure. The individual on the RB side, who was using the security card reader, saw the RB door pop open. The doors were immediately closed, reestablishing secondary containment.

Investigation identified that the latch on the RB side door appeared to be sticking (e.g. not fully returning to the latched position once released) when the crash bar was engaged.

CAUSE OF EVENT

The cause was determined to be sticking of the RB side door latch inside the crash bar, which prevented the door from properly latching and staying latched when differential pressure was applied, such as when the TB side door was opened. The most likely cause of the crash bar latch failing to reset properly is abnormal wear from heavy use during outage mobilization exacerbated by mechanical damage suffered during impacts with wheeled carts carrying material through the airlock.

ANALYSIS/SAFETY SIGNIFICANCE

An engineering evaluation was performed and concluded that secondary containment could have performed its safety function of isolating as assumed in the accident analysis and also of re-establishing 0.25 inches vacuum (drawdown) within the assumed accident analysis time (10 minutes). Therefore, the subject event did not cause a loss of safety function. This event will not be counted as a safety system functional failure (SSFF) for the NRC performance indicator based on the engineering analysis that shows there was no loss of ability to fulfill the safety function.

comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.